1. Field of the Invention
The present invention relates to a spin-valve magnetoresistive element in which electrical resistance changes in response to the relationship between the magnetic direction of a pinned magnetic layer and the magnetic direction of a free magnetic layer which is influenced by an external magnetic field, and more particularly relates to a spin-valve magnetoresistive element in which the magnetizations of a pinned magnetic layer and a free magnetic layer are properly put into single magnetic domain states so that Barkhausen noise is reduced and satisfactory micro-track-asymmetry can be obtained.
2. Description of the Related Art
FIG. 4 is a sectional view which shows the conventional structure of a spin-valve magnetoresistive element (spin-valve magnetoresistive head) which detects a recording magnetic field from a recording medium such as a hard disk.
This spin-valve magnetoresistive element includes an antiferromagnetic layer 1, a pinned magnetic layer 2, a non-magnetic electrically conductive layer 3, and a free magnetic layer 4 deposited in that order, and hard bias layers 5 and 5 formed on both sides thereof.
Generally, an iron--manganese (Fe--Mn) alloy film or a nickel--manganese (Ni--Mn) alloy film is used for the antiferromagnetic layer 1, an iron-nickel (Fe--Ni) alloy film is used for the pinned magnetic layer 2 and the free magnetic layer 4, a copper (Cu) film is used for the non-magnetic electrically conductive layer 3, and a cobalt--platinum (Co--Pt) alloy film or the like is used for the hard bias layers 5 and 5. Also, an underlying layer 6 and a protective layer 7 are composed of a non-magnetic material, for example, tantalum (Ta).
As shown in the drawing, the antiferromagnetic layer 1 and the pinned magnetic layer 2 are formed in contact with each other, the pinned magnetic layer 2 is put into a single magnetic domain state in the Y direction by an exchange anisotropic magnetic field caused by exchange coupling at the interface between the pinned magnetic layer 2 and the antiferromagnetic layer 1, and the magnetic direction is pinned in the Y direction. The exchange anisotropic magnetic field occurs at the interface between the antiferromagnetic layer 1 and the pinned magnetic layer 2 by annealing (heat treatment) while applying the magnetic field in the Y direction.
Also, the magnetic direction of the free magnetic layer 4 is aligned in the X direction under the influence of the hard bias layers 5 and 5 which are magnetized in the X direction.
A method for fabricating the spin-valve magnetoresistive element shown in FIG. 4 includes the steps of depositing six layers from the underlying layer 6 to the protective layer 7, scraping the sides of the six layers so as to have inclined edges in the etching process, for example, by ion-milling, and then, depositing hard bias layers 5 and 5 on opposite sides of the six layers.
In the spin-valve magnetoresistive element, a stationary electric current (sensing current) is applied from electrically conductive layers 8 and 8 formed on the hard bias layers 5 and 5 into the pinned magnetic layer 2, the non-magnetic electrically conductive layer 3, and the free magnetic layer 4. The driving direction of a recording medium such as a hard disk is in the Z direction, and if a magnetic field leaked from the recording medium is applied in the Y direction, the magnetization of the free magnetic layer 4 changes from the X direction to the Y. Because of the relationship between the change in the magnetic direction in the free magnetic layer 4 and the pinned magnetic direction of the pinned magnetic layer 2, the electrical resistance changes, and the magnetic field leaked from the recording medium can be detected by the voltage change based on the change in the electrical resistance.
In the conventional spin-valve magnetoresistive element shown in FIG. 4, however, there are the following problems.
As described above, although the magnetization of the pinned magnetic layer 2 is pinned in the Y direction (shown in the drawing), the hard bias layers 5 and 5 magnetized in the X direction are provided on both sides of the pinned magnetic layer 2. Therefore, the magnetization of, in particular, both ends of the pinned magnetic layer 2 is influenced by the bias magnetic field from the hard bias layers 5 and 5, and is not pinned in the Y direction (shown in the drawing).
That is, in the spin-valve magnetoresistive element, it is preferable that the magnetization of the pinned magnetic layer 2 and the magnetization of the free magnetic layer 4 be put into single magnetic domain states in the Y direction and in the X direction, respectively, and that the magnetization of the pinned magnetic layer 2 be orthogonal to that of the free magnetic layer 4 in the entire region. However, the magnetization relationship between the pinned magnetic layer 2 and the free magnetic layer 4 around both ends is not orthogonal because the magnetization of the pinned magnetic layer 2 is not pinned in the Y direction, and satisfactory micro-track-asymmetry cannot be obtained around both ends. The word "micro-track-asymmetry" means the vertical asymmetry of the regenerated output waveform measured in a track width which is smaller than the real track width.
If the regenerated output value has the same height at every part when micro-track-asymmetry is measured, the micro-track-asymmetry is considered to be in a satisfactory condition. However, when the micro-track-asymmetry is measured around both ends of the pinned magnetic layer 2 and the free magnetic layer 4 shown in FIG. 4, the regenerated output value has non-uniform height. That is, the micro-track-asymmetry is in the deteriorated condition, which makes it difficult to detect the track position accurately and easily leads to a servo error.
Also, in addition to the above-mentioned problem, in the spin-valve magnetoresistive element shown in FIG. 4, the hard bias layers 5 and 5 provided on opposite sides of the free magnetic layer 4 are substantially thin, and thus, a sufficient bias magnetic field cannot be applied from the hard bias layers 5 and 5 to the free magnetic layer 4 in the X direction. Accordingly, the magnetic direction of the free magnetic layer 4 is not stabilized easily in the X direction, and Barkhausen noise easily occurs.